It is well known that water-absorbing polymers have various utilities and have been used in various applications such as hygienic supplies (sanitary goods, diapers, etc.), agricultural and horticultural equipment (water-retaining agent) and those applications which require water-retaining properties.
As the water-absorbing polymers, various polymers have been known, such as starch-based polymers, poval-based polymers, cellulose-based polymers and the like. Among these, however, secondary products obtained by processing powdery or fibrous materials are efficiently put to practical use. More particularly, in the absence of suitable plasticizers, conventional water-absorbing polymers by themselves have not been able to be molded into the shape of a sheet or the like. For example, powdery materials have to be carried on a fibrous base material such as paper or nonwoven fabric before molding (e.g., Examined Publication No. 6-78402, Japanese Patent Application Laid-Open No. 52-143710, etc.). In such molded products from carried powdery water-absorbing polymer, the water-absorbing sites are water-absorbing polymer which are scattered or dotted in the molded product and, hence, the molded products show only a limited water absorbency and has a low liquid absorbency for ionic and water-soluble organic solvent-containing solutions. Furthermore, the molded products are complicated and costly to manufacture.
To solve the above-described problems, there has been disclosed a method for preparing a film- or fiber-shaped water-absorbing composition using a hydrophilic polymer obtained by copolymerizing carboxyl group-containing monomers (cf., Japanese Patent Application Laid-Open No. 1-103643, and Japanese Patent Application laid-Open No. 56-79122). However, no suitable plasticizer therefor was available and the films obtained were so hard and brittle that they were not put into practical use for some applications. On the other hand, Japanese Patent Application Laid-Open No. 1-103643 discloses a method in which polyvinyl alcohol and a carboxyl group-containing copolymer are used as a hydrophilic polymer and polyhydric alcohol is used as a plasticizer. This method, however, has a problem that the polyvinyl alcohol bleeds out after absorbing the liquid since the polyvinyl alcohol and the alcohol do not have sufficient affinity for each other and the polyvinyl alcohol does not participate in crosslinking. Further, in order to obtain by the technique a liquid (sol form) which is flexible enough to be molded, it is necessary to dilute the composition with water and, as a result, to vaporize the water upon molding, so that the manufacture of a molded product has taken considerable time.
Therefore, an object of this invention is to provide a composition which is free of the problems encountered by the conventional water-absorbing molded products containing a liquid-absorbing polymer in a dispersed state, i.e., a liquid-absorbing material composition which has an improved water absorbency so that every part of the composition can absorb water.
Another object of this invention is to provide a liquid-absorbing material composition that has an elevated liquid-absorbing efficiency for ion-containing water, water-soluble organic solvent-containing liquid or alcohols.
Still another object of this invention is to provide a liquid-absorbing material composition having flexibility so that it can easily be molded into a sheet or the like and an improved gel strength after absorbing a liquid.
Yet another object of this invention is to provide a molded product of liquid-absorbing material comprising such a liquid-absorbing material composition crosslinked to have any desired shape and a method for manufacturing such a molded product.
Further, an object of this invention is to provide various uses of such a molded product of liquid-absorbing material.